1. Field of the Invention
Embodiments of the present invention generally relate to a chemical mechanical polishing system. In particular, embodiments of the present invention relate to a method and apparatus for monitoring a polishing surface conditioning mechanism of a chemical mechanical polishing system.
2. Description of the Related Art
Chemical mechanical polishing is one process commonly used in the manufacture of high-density integrated circuits. Chemical mechanical polishing is utilized to planarize a layer of material deposited on a semiconductor substrate by moving the substrate in contact with a polishing surface while in the presence of a polishing fluid. Material is removed from the surface of the substrate that is in contact with the polishing surface through a combination of chemical and mechanical activity.
In order to achieve desirable polishing results, the polishing surface must be periodically dressed, or conditioned. One type of conditioning process, typically performed on the polyurethane polishing pads traditionally utilized in chemical mechanical polishing, is configured to restore the fluid retention characteristics of the polishing surface and to remove embedded material from the polishing surface. Another type of conditioning process, typically performed on fixed abrasive polishing materials, is configured to expose abrasive elements disposed within structures comprising the abrasive polishing material, while removing asperities from the upper surface of the polishing material and leveling the structures comprising the polishing surface to a uniform height.
In one embodiment, a polishing surface conditioner includes a replaceable conditioning element, such as a diamond disk, coupled to a conditioning head that is movable over the polishing surface. The conditioning element is lowered into contact with the polishing surface while being rotated. The conditioning head is generally swept across the rotating polishing surface to allow the conditioning element to condition a predefined area of the polishing surface.
Conventional conditioners commonly utilize diaphragms within the conditioning head to control the elevation of the conditioning element. A cavity behind the diaphragm is generally pressurized to lower the conditioning element and press it against the polishing surface of the polishing pad during conditioning. Upon completion of conditioning, the cavity is vented, allowing the conditioning element to retract, typically assisted by an upward spring bias.
The pressurization and the venting of the cavity causes the diaphragm to repeatedly stretch and relax. In addition, the raising and lowering of the conditioning element further applies stress to the diaphragm. However, the elastomeric diaphragm, like all other elastomeric materials have a finite life. Without repair or replacement, the eventual deterioration of the diaphragm leads to poor conditioning. To prevent the inevitable deterioration, the diaphragm is typically replaced on a set interval, for example after a preselected number of conditioning cycles. However, the conventional method is inefficient. Sometimes, the diaphragm will be replaced while it is still in good condition, causing unnecessary downtime and increasing costs. At other times, a diaphragm in poor condition is not replaced soon enough, causing poor conditioning of the pad.
Therefore, there is a need for a method and apparatus for monitoring pad conditioning mechanisms.